This invention relates generally to a parking brake for a rail vehicle braking system, and more particularly to a parking brake which can automatically lock the brakes on the rail vehicle in an applied position responsive to a brake application. The parking brake can be configured for use on both truck and car mounted rail car brake systems.
Freight car handbrakes provide two distinct functions, both important. One is to serve as a parking brake to prevent a car or cut of cars from moving when detached from a locomotive. The other is to serve as a manual speed-control brake on slow moving cars, as is often done with bulk commodity cars. While the conventional handbrake, as an individual car-based system, meets both sets of service requirements, this utility comes at a high cost. Both the normal use and the misuse of handbrakes generate substantial costs for railroads and/or car owners, in several different ways, including failure of a crewman to release a handbrake after normal use as a parking brake, mishaps during normal use as a parking brake, and time lost in waiting for a crewman to walk to, operate, and return from operation of the handbrake. The normal operational use of handbrakes on individual cars is both time consuming and labor intensive, and mishaps resulting from the task of setting and releasing handbrakes during such normal use accounts for a relatively high incidence of personal injury claims and lost time. Misuse, such as dragging cars with unreleased handbrakes is a pervasive, industry-wide problem that leads to inordinate numbers of wheelset changeouts and related equipment downtime. Additionally, trickle-down damage, such as from slid-flat wheels, create impacts on the rail and car that can damage equipment and lading, and increase both track and equipment maintenance costs.
The operation of a handbrake requires the presence of a trainman at that particular car; and the time for him to reach the car, operate the device, and move to another car or return is considerable. Later on, when the handbrake should be released, this time requirement is imposed a second time. Where remote-controlled locomotives are used, the entire switching operation must be held up until sufficient handbrakes are set to hold a car or group of cars. The tasks of setting up handbrakes every time cars are parked and then locating and releasing them when such cars are to be moved thus consumes substantial time and labor, which is a costly drain on railroad operations and productivity.
Parked cars must be secured, but the requirement that trainmen twice visit each car location in order to do so could be eliminated and the system effectiveness improved if a train-based system could be used rather than car-based equipment.
An automatic parking brake as described hereinafter could alleviate many of the problems and costs associated with handbrake use. Such a parking brake can be applied automatically, anytime cars are parked, and can also be released automatically when desired. Both the setup and release can be carried out without leaving the locomotive, and the holding power of the parking brake on any one car will be similar to that of the manual handbrake. Furthermore, and quite importantly, if empty cars are moved without releasing the parking brake, it will not normally result in any wheel sliding.
Accordingly, widespread implementation of such an automatic parking brake could eliminate a major portion of the problems and related costs associated with handbrake usage today, including wheel damage, secondary rail and equipment damage, time and labor requirements and injury claims. Moreover, in addition to resolving such existing problems as described previously, the automatic parking brake can also provide a measure of added safety for grade operations. For example, the automatic parking brake makes it easier to secure trains stopped on a grade and essentially provides a mechanical backup to the pneumatic emergency brake. Ultimately, each of these improvements in operating efficiency would directly impact train crew responsibilities and requirements.
A typical rail car hand brake system normally consists of an apparatus for manually applying and biasing one or more brake shoes against the tread of one or more wheels of the rail car by either turning a hand wheel or pumping a ratchet handle on a hand brake mechanism attached to the rail car. In both truck and car mounted rail car braking systems (illustrated in FIGS. 1–3), the hand brake mechanism is usually either a cast or stamped metal gear housing, and is typically attached to an outside end wall of the rail car. A rotatable chain drum must be rotated by turning the hand wheel to wind a brake chain onto the chain drum. The other end of the brake chain normally extends through the bottom of the gear housing and is interconnected with cable or other linkage, such as a hand brake lever, to the brake beams which carry the brake shoes. The winding of the brake chain onto the chain drum applies tension to the brake chain and brake linkage to draw the brake shoes against the tread surfaces of adjacent rail car wheels and, accordingly, applies the hand brake as intended.
A disadvantage of this prior art type hand brake arrangement is that train operators must manually apply the parking brake on each car to be left standing alone. When coupled groups of cars are to be left, it is up to the operator's judgment how many of the handbrakes must be set, and how hard the hand wheel must be turned to set them. This requires a considerable amount of time and labor. Additionally, the operators must be certain that the hand wheel is turned a sufficient amount to ensure that the parking brake is engaged. The possibility also exists that an operator may forget to apply the brake altogether on a rail car, which could result in unexpected movement of the rail car while parked at the siding or yard. Alternatively, wheel damage can result due to a failure to release the handbrake from the applied position before the car is to be moved. Operation of the hand wheel also requires exerting a considerable amount of physical force from a sometimes awkward position, which can make the hand brake difficult to apply. Injuries to operators also sometimes occur related to hand brake use, primarily due to slipping and tripping, but injuries due to overexertion have also been noted. Furthermore, since brake cylinder pressure can leak over time, a potentially hazardous condition can develop if a loss of brake cylinder pressure occurs subsequent to an emergency brake application, and particularly if the train is stopped on a grade.
A loaded brake engagement mechanism has been used in Type AB-8 and AB-10 Manual Empty and Load Freight Car Brake Equipments, manufactured By Westinghouse Airbrake Technologies, Inc., the assignee of the present invention. As described in Instruction Pamphlet 5062-2 Sup. 1, dated May 1942, this mechanism incorporated a telescoping housing, hollow rod and push rod arrangement inside a specially designed “UL” type brake cylinder, called a “load brake cylinder” which was used to make a loaded brake application. The load brake cylinder was one of two separate brake cylinders on the rail vehicle, the other being an “empty brake cylinder,” which were used to control the application of brakes on the rail vehicle. The piston push rods of each brake cylinder were connected to a common lever, called the live cylinder lever, which was connected to the brake rigging on the rail car. In the load brake cylinder, the push rod telescoped within a hollow tube, and through a housing fastened to the end of the hollow rod the relationship between the hollow rod, & housing and the push rod was regulated by a ratcheting mechanism carried in the housing which cooperated with notches in the push rod and which carried a ratchet release trigger whose operation will be explained. During a loaded brake application, the empty brake cylinder would operate and, via the connection of the push rods of both the empty and load brake cylinders to the live brake cylinder lever, the push rod of the load brake cylinder would be pulled from the hollow rod as a result of force exerted on, and motion imparted to the push rod of the empty brake cylinder by its pressurization. The ratcheting mechanism was not operational in the release position of the load cylinder because in this position the release trigger was tripped. The load cylinder pushrod thus telescoped unimpeded out from the housing during the movement of the empty cylinder's piston and hollow rod. When, in the loaded car condition, the empty brake cylinder reached maximum extension of the push rod, the load brake cylinder could be pressurized through a special load sensing valve, which caused the load cylinder's hollow rod and housing to extend.
Extension of the housing containing the ratcheting mechanism would operate the ratchet trigger as soon as the housing moved away from the load cylinder body, and the now effective ratchet would prevent the push rod from returning to its telescoped position relative to the housing as the housing advanced under the influence of load cylinder pressurization. The push rod was thus caused to extend an additional amount along with the housing, thereby increasing the braking force. Basically, the telescoping function of the load cylinder push rod with respect to the housing, controlled via the ratcheting mechanism, permitted the application of additional piston force at a further distance from the pivot point of the live cylinder lever, without using an appreciable amount of air over and above that required for the empty cylinder, thus increasing the force delivered by this lever to the brake shoes at little price in air consumption as compared with an empty brake application.
When he brake was released, the ratchet mechanism, absent the release trigger, would have prevented the release of the shoes, because the load cylinder, even in release position, would have held its pushrod extended and thus held the live cylinder lever in its fully applied—empty car state.
This undesirable state of affairs was prevented by the operation of the ratchet release trigger operating as a result of the return of the hollow rod to its release position bringing the trigger back into contact with the cylinder's non-pressure head, tripping the ratchet release, and permitting the load cylinder pushrod to withdraw into the housing and hollow rod. This mechanism, however, was not a parking brake and could not address the disadvantages listed above.
A rail vehicle parking brake which is adapted to address such disadvantages of conventional rail vehicle parking brakes is described in co-pending U.S. patent application Ser. No. 10/438,141, assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference.
Further embodiments of a parking brake for a rail vehicle which can be applied automatically to lock the brakes on the rail vehicle are disclosed hereinafter.